This invention relates to apparatus for conducting ocular plethysmography (OPG) tests by noninvasive means.
The recognition of extracranial carotid occlusive disease as a major remediable cause of strokes in persons has resulted in increased research into means and methods whereby flow reducing lesions of the internal carotid artery may be detected. Potential stroke candidates create a need for effective noninvasive means to improve the selection of patients for surgical intervention.
The left and right common carotid arteries which are located on opposite sides of the neck and lower face, each bifurcate into the internal carotid artery running to the same sided eye and external carotid artery to the same sided ear. The internal carotid artery additionally supplies blood to the same side of the brain. It has been known that occlusive plaque may build up at this bifurcation, creating a stenosis which tends to reduce the passage of blood through the arteries. This reduced blood flow results in a delay of blood flow pulses sensed at the eye and ear. Delays between similarly situated points on pulsatile wave forms at each eye and each ear is indicative of this occlusive plaque buildup. Should there be equal occlusive plaque buildup in each internal carotid artery, ideally, similarly situated points on the waveform, i.e., crest or trough, at each eye would be the same. However, extracranial carotid occlusive disease of equal severity is relatively rare. Therefore, in most cases, in the presence of the disease, there will be unequal delays in similarly situated points upon the waveform pulsatile waves at the eyes indicative of varying degrees of severity of the disease.
There have been a number of papers written and inventions made in this field, such as for example, Oculoplethysmography; An Adjunct To Arteriography In The Diagnosis Of Extracranial Carotid Occlusive Disease, American Journal of Surgery, Vol. 132, December 1976, Kartchner, McRae, Crain, and Whitaker, and U.S. Pat. No. 3,911,903, William Gee, et al. The Patent of Gee describes method and apparatus for determining blood pressure pulse waves at the eye under varying vacuum conditions, but utilizes large amounts of apparatus together with extremely complicated means attempting to isolate one eye and its associated transducer from the other eye and its associated transducer, and never completely isolates different eye-transducer communication mediums.